EXPIRATORY CT SCANS FOR CHRONIC AIRWAY DISEASE - CORRELATION WITH PULMONARY-FUNCTION TEST-RESULTS

OBJECTIVE. The purpose of our study was to correlate findings on expir atory CT scans with results of pulmonary function tests (PFTs) and to determine whether these techniques may be complementary in assessing a irway obstruction. MATERIALS AND METHODS. Seventy-four patients with s uspected chronic airway disease and 10 healthy nonsmokers underwent in spiratory and expiratory CT scans and PFTs. An air trapping score, cor responding to the ratio of the cross-sectional air trapping area versu s the total cross-sectional lung area on expiratory CT, and a reductio n score, representing the change in cross-sectional lung area at inspi ration and expiration, were calculated using a quantitative grid. The two scores were then correlated with the results of the PFTs. RESULTS, Expiratory air trapping was seen in 18 (51%) of 35 patients with seve re airway obstruction (forced expiratory volume in 1 sec [FEV1]:vital capacity < 80%) (group A), in 21 (72%) of 29 patients with predominant ly small airways obstruction (abnormal flow-volume curve and FEV1:vita l capacity greater than or equal to 80%) (group B1), and in four (40%) of 10 patients with normal PFT results (group B2). Expiratory air tra pping was never seen in the 10 healthy subjects. Air trapping scores w ere 27%, 12%, and 8% for groups A, B1, and B2, respectively, with sign ificant negative correlations with FEV1 (r = -.45), FEV1:vital capacit y (r = -.31), and forced expiratory flow at 25% of vital capacity (r = -.57). Reduction scores were 18%, 30%, 35%, and 43%, for the groups A , B1, B2, and the healthy group, respectively, with significant correl ations with all the PFT indexes (r = .35 to .66) except total lung cap acity. CONCLUSION. Air trapping may permit detection of airway obstruc tion in patients with clinically suspected chronic airway disease even when PFTs are normal. Furthermore, expiratory CT allows one to calcul ate a reduction score for a cross-sectional lung area that appears to be better correlated with the degree of airway obstruction measured on PFTs.